When a fault current occurs, especially an overcurrent, or when a short-circuit or an arcing fault occurs, the current-breaking capacity and turn-off time of a power breaker are dependent on various parameters. The turn-off process is made up of the tripping time, the inherent delay and the turn-off time. The tripping time is the time from the occurrence of the variable that causes the tripping until the initiation of the tripping process, for instance, the release of a breaker latch. This is followed by the inherent delay of the circuit breaker, which is determined by the dynamic processes of the contacts of the circuit breaker as they move and open. A turn-off time of about 30 to 50 msec is expected in a circuit breaker for the higher power range (rated current up to 6300 A).
Severe injury to persons and/or material damage can result from the occurrence of an arcing fault in an electrical installation, so this should be prevented to the greatest extent possible. In order to limit such injury or damage, several measures have been proposed, of which the optimal solution is to interrupt (to extinguish) the arcing fault in a shorter time than the turn-off time of the incoming circuit breaker.
It is a known procedure to use short circuiters to interrupt arcing faults in electrical installations. Various systems that detect physical effects of the burning arc (light, sound, pressure) can be used in such an arrangement for extinguishing an arcing fault. A proven system is based on the optical detection of an arc (EP 0575 932 B1). In order to switch off the arc, various short circuiter arrangements are proposed, for example, the use of a pyrotechnically driven short circuiter (EP 1052 665 B1 or WO 200062320 A1), by means of a short-circuit to be produced by thyristors (DE 4438593 A1) or by using a vacuum interrupter (DE 4404074 A1). Such short circuiters produce a short-circuit between the phases of the electric power system, between which the arc burns, so that the arcing fault can be extinguished within a period of time shorter than 3 msec.
After the short circuiter has been tripped, a short-circuit current is still flowing that is interrupted by the serially connected incoming circuit breaker (after its turn-off time), as a result of which the defective electrical installation is ultimately disconnected from the electric power system.
The advantage of an arc detection and extinguishing system is obvious. However, the special effort involved in the installation of an optical arc detection system with optical waveguides and corresponding opto-electronics is quite considerable. Consequently, in some electrical installations, the use of an arc detection and extinguishing system is sometimes dispensed with for cost reasons—in spite of the obvious advantages.